1. Field of the Invention
This invention relates to a wobble detecting apparatus for detecting a wobble signal of an optical disk in a device for recording and/or reproducing information for the optical disk.
2. Description of the Related Art
In an optical disk such as a writable CD or DVD, as shown in FIG. 10, a track 1A of an optical disk 1 on which information is to be stored wobbles. The wobble is detected to reproduce a clock signal at the time of the write.
In the device for recording and/or reproducing information for the optical disk, as the case may be, the presence or absence of the wobble is decided to determine whether the optical disk loaded in the device is recordable or dedicated to only reproduction.
In the device for recording and/or reproducing information for an optical disk, laser light is focused, the focused light is projected on the optical disk, and the light reflected from the optical disk is received by a light receiving element, thereby providing a wobble signal, a tracking signal, a focus signal and a reproduction signal.
FIG. 11 shows relative positions of a light receiving element and a received light spot 21 of the reflected light projected on the light receiving element 4.
The light receiving element 4 is partitioned into four sections A, B, C and D. In shipping the device, as seen from FIG. 11B, adjustment is made so that the received light spot is projected on the center of the four divided sections. This adjustment cannot be made completely. As seen from FIG. 11A, the optical axis is misaligned leftward, or otherwise, as seen from FIG. 11C, the optical axis is misaligned rightward.
The wobble signal is obtained from a difference signal (A+B)xe2x88x92(C+D) on the basis of the output signals from the sections A, B, C and D of the light receiving element 4.
As seen from FIGS. 11A and 11C, when the received light spot deviates from the boundary between the sections A, B and C, D owing to the misalignment of the optical axis, the S/N ratio of the wobble signal based on the difference signal (A+B)xe2x88x92(C+D) is deteriorated, and hence the presence or absence of the wobble signal cannot be detected precisely.
An object of this invention is to provide a wobble signal detecting apparatus which can detect the presence or absence of a wobble.
In order to attain the above object, in accordance with an aspect of this invention, there is provided a wobble detecting apparatus for a device for recording and/or reproducing information for an optical disk, comprising:
a wobble detecting unit for detecting a wobble on the basis of a signal from a light receiving element which receives light reflected from the optical disk;
an offset voltage generating unit for generating an offset voltage;
an adder unit for adding the offset voltage to a control signal to an actuator for the optical disk;
an actuator switch for on/off controlling a control signal to the actuator; and
a control unit for turning on the actuator for wobble detection to decide whether or not the wobble has been detected by the wobble detecting unit, and if the wobble has not been detected, causing the offset voltage generating unit to generate a positive or negative prescribed voltage to decide further whether or not the wobble has been detected by the wobble detecting unit.
In a preferred embodiment, where the wobble has not been detected by the wobble detecting unit when the positive or negative prescribed voltage is generated by the offset voltage generating unit, the control unit causes the offset voltage generating unit to generate a new offset voltage of the prescribed voltage plus the offset voltage previously produced, thereby causing the wobble detecting unit to repeat the wobble detection by a prescribed number of times.
In accordance with another aspect of this invention, there is provided a wobble detecting apparatus for a device for recording and/or reproducing information for an optical disk, comprising:
a wobble detecting unit for detecting a wobble on the basis of a signal from a light receiving element which receives light reflected from the optical disk;
an offset voltage generating unit for generating an offset voltage;
an adder unit for adding the offset voltage to a control signal to an actuator for the optical disk;
an actuator switch for on/off controlling a control signal to the actuator;
an carriage switch for on/off controlling a control signal to a carriage on which the actuator is loaded; and
a control unit for turning on the carriage switch turning on the actuator for wobble detection and causing the offset voltage generating unit to generate a prescribed voltage to decide whether or not the wobble has been detected by the wobble detecting unit.
In a preferred embodiment of another aspect of this invention, the control unit counts the number of rotation of the optical disk from when wobble detection is started, and confirms non-detection of the wobble if the wobble has not detected when the counted value reaches a prescribed number of times.
In accordance with still another aspect of this invention, there is provided a wobble detecting apparatus for a device for recording and/or reproducing information for an optical disk, comprising:
a wobble detecting unit for detecting a wobble on the basis of a signal from a light receiving element which receives light reflected from the optical disk;
a low pass filter for passing a DC component of a difference signal produced from the light emitting element;
an offset voltage generating unit for generating an offset voltage;
an adder unit for adding the offset voltage to a control signal to an actuator for the optical disk;
an actuator switch for on/off controlling a control signal to the actuator; and
a control unit for turning off the actuator for wobble detection, causing the offset voltage generating unit to generate the offset voltage so that an output form the low pass filter is zero, turning on the actuator switch when the output from the low pass filter has become approximately zero, and deciding whether or not the wobble has been detected by the wobble detecting unit.
In accordance with this invention, an actuator is moved to realize the state with no misalignment of an optical axis, and in this state, a wobble is detected. Therefore, S/N can be improved and the presence or absence of the wobble can be detected accurately.
The above and other objects and features of the invention will be more apparent from the following description taken in conjunction with the accompanying drawings.